Power management systems are widely used in modern technology for different purposes as supervising the power consumption in an electrical system, preventing overloading, etc. At the load side there can be a battery for example. So when there is a charger, the battery will be considered the load, but when there is no charger and the battery has to supply some kind of accessory, then the battery is the power generator. So it depends on the application and the situation on what side is the power generator and on what side is the load.
U.S. Pat. No. 6,215,338 describes a monitoring of low currents through a DMOS driver i.e. a monitoring system of an output stage of a power amplifier. A feedback circuit is responsive to a voltage applied to a gate of the DMOS power transistor to limit the minimum value to which the drain-source voltage may drop to keep it sufficiently high, and to allow a reliable monitoring of the current through the power transistor, even at relatively low levels. This is performed by increasing the conduction resistance of the power transistor at low current levels. It is observed that the source of the DMOS transistor is connected to a reference terminal i.e. it is grounded. Furthermore, there is no indication on an inverse current through the transistor. It should be pointed out that in applications, as battery charging, it is desirable to monitor a floating current i.e. not related to a reference terminal as ground, the current circulating either from a source to a load or vice versa. The solution provided by the prior art could, therefore, not be applied mutatis mutandis to a power management system for a floating current.